1. Field of the Invention
The present invention relates to a navigation device which indicates the characteristics of a tunnel on the display before entering the tunnel when a vehicle""s approach to the tunnel is detected using a navigation function. The safety and comfort of the driver are maintained by displaying a precaution with respect to conditions resulting from entering the tunnel.
2. Description of the Related Art
FIG. 1 shows a conventional navigation device as disclosed for example in JP-A-10-100815. The navigation device is adapted to detect a vehicle""s approach to a tunnel and activate various on-vehicle devices in a tunnel mode function on the basis of the detected signal.
In FIG. 1, reference numeral 1 denotes a navigation computer means with a database (not shown). Map data is stored in the database, the map data includes data on the accurate position of tunnels as well as data on a road network, which can be travelled on by the vehicle, and the road network surroundings.
Reference numeral 2 is a GPS antenna, 3 is a vehicle position detection means, 4 is a control means which controls the operation of the on-vehicle devices based on the output signal from the navigation computer means 1. Reference numeral 5 is a window operation means provided with a motor, 6 is a headlight control means, 7 is a sunroof operation means, 8 is an air conditioner switching means which switches an air circulation mode, 9 is a manual tunnel switch for controlling the activation of each means manually based on the display command from the control means 4 with respect to the tunnel mode function.
Next, the operation of the conventional navigation device will be described.
The navigation computer means 1 determines a vehicle position continuously on a road network on the basis of a GPS satellite signal from a GPS antenna and an output signal of the vehicle position detection means 3. From the continuously obtained position, the navigation computer means 1 confirms whether the vehicle is currently traveling inside or outside a tunnel on a searched route. If the vehicle is currently inside a tunnel, the navigation computer means 1 confirms whether the vehicle has just entered the tunnel or has just finished travelling through the tunnel.
When it is determined that the vehicle is about to enter the tunnel, an appropriate message signal is transmitted to the control means 4. The control means 4 selects on-vehicle devices to be activated in a tunnel mode function in response to the transmitted signal and automatically activates the tunnel mode function. Alternatively, a display suggesting operation of the manual tunnel switch 9 is performed. A driver operates the manual tunnel switch 9 based on this display and various types of on-vehicle equipment are activated in the tunnel mode function.
For example, such a tunnel mode function includes,
(1) Closing the windows by activation of the window operation means 5,
(2) Closing the sunroof by activation of the sunroof operation means 7,
(3) Activating the headlight control means 6 to lower the beam of the headlights for example,
(4) Placing the air-conditioner in air recirculation mode by activation of the air-conditioner switching means 8,
(5) Switching over an audio system from radio reception mode to recorded medium mode.
Since the conventional navigation device is constructed as the above, on-vehicle devices are activated in a tunnel mode function or are placed in an operable state for the tunnel mode function if it is confirmed that a vehicle will enter a tunnel on a currently traveled searched route. However, for example even in those cases when the tunnel is short and it is not necessarily required to activate the tunnel mode function or place the on-vehicle devices in an operable state for the tunnel mode function, various on-vehicle devices are switched intermittently between the tunnel mode and the other modes. Thus, the possibility exists that the durability of the on-vehicle devices will be reduced as a result of the frequent switching operation.
Furthermore, the problem has arisen that even when the tunnel mode function is activated, since information such as the length of the tunnel, lane number, presence of traffic signals in the tunnel is not known, the driver has to enter the tunnel in a tense, uneasy state. In particular, if the inside of the tunnel is sloping and the road extends in a descending slope towards the tunnel exit, vehicle speed will naturally increase. Furthermore, when the road curves at the tunnel exit, the possibility exists of dangerous conditions.
The present invention is proposed to solve the above problems and has the object of providing a navigation device which performs a precautionary function by informing characteristics of a tunnel to a driver before entering the tunnel when a vehicle encounters a tunnel. Such characteristics include for example, the name of the tunnel, the shape of the tunnel (length, height, width, presence of curves), the lane number, and the presence of traffic lights or the like.
The navigation device according to the present invention comprises: a vehicle position detection means for detecting a vehicle position; a vehicle speed detection means for detecting a vehicle speed; a determination means provided with a database which records data on a currently traveled route network, data on the surroundings thereof, and characteristic data relating to tunnels on the route network, the determination means determining whether or not to activate a tunnel mode function on the basis of the characteristic data relating to the tunnel read from the database, the vehicle speed detected by the vehicle speed detection means and the vehicle position detected by the vehicle position detection means; and a control means for displaying characteristics of the tunnel to be travelled through on a display means based on a command signal from the determination means indicative of activation of the tunnel mode function and for activating each on-vehicle device in the tunnel mode function or suggesting activation of the tunnel mode function.
In this way, when a vehicle approaches a tunnel, the characteristics of the tunnel are indicated on the display section of the navigation device and it is possible to comprehend the characteristic conditions of the tunnel beforehand. As a result, the decisions whether to illuminate headlights, turn off wipers, close windows, and switch the air-conditioner to air recirculation mode can be performed with a degree of ease. Thus, driving comfort and driving safety are increased.
Further, the navigation device of the present invention is adapted to determine whether to activate a tunnel mode function in consideration of the vehicle speed and the displayed information about the tunnel, and to automatically activate various on-vehicle devices in the tunnel mode function or display the suggestion to activate the tunnel mode function in order to instruct a driver to operate the manual tunnel switch. As a result, it is possible to avoid unnecessary mode switching in comparison with the conventional navigation device which switches the mode of the on-vehicle devices on each occasion to enter a tunnel. Therefore, damage due to frequent mode switching of various on-vehicle devices can be reduced
The navigation device of the present invention may be adapted to display a longitudinal sectional view of the tunnel through which the vehicle will travel on a display section of the navigation means when the tunnel mode function is activated.
In such a way, it is possible to indicate a slope of the road in the tunnel. Thus, it is possible to drive according to the road conditions, as a result, driving safety can be improved.
The navigation device of the present invention may be adapted to display characteristic information relating to the tunnel through which the vehicle will travel on a display section of the navigation means.
In such a way, it is possible to indicate tunnel conditions to the driver beforehand. Therefore, it is possible to improve driving safety and comfort as a result of the extra time allowed for determining required actions.
Furthermore, the navigation device of the present invention is adapted to calculate a distance to a tunnel based on a vehicle speed detected by a vehicle speed detection means when the vehicle lies within a link area in map data on which the tunnel exists. When the distance is within a fixed value, characteristics relating to the tunnel through which the vehicle will travel are displayed on the display section of the navigation means.
In such a way, it is possible to perform display of tunnel characteristics in an appropriate timeframe in consideration of vehicle speed.
The navigation device of the present invention may be adapted to determine whether or not to guide a tunnel based on the tunnel length and an average vehicle speed before entering the tunnel.
In such a way, it is possible to prevent unnecessary tunnel guiding.